1. Field of the Invention
This invention relates to a method and a system for the disposal of waste and/or hazardous materials waste.
2. Description of the Prior Art
A major problem facing modern society is the disposal of toxic waste and/or hazardous materials in a manner which minimizes harmful effects on the environment. Such a disposal system is one which is capable of reducing such toxic and/or hazardous waste to compounds which are suitable for environmental disposal. Such suitability is, of course, defined in terms of acceptable levels of pollution, and is determined by a variety of regulatory agencies.
Traditionally, hazardous waste disposal has taken the form of direct burial in landfills, or simple thermal processing of the waste, followed by burial of the solid residue, and release to the atmosphere of the volatile residue. None of these approaches have proven acceptable, due to the fact that the materials which are released to the environment tend to remain as unacceptable sources of pollution.
Another normal approach for a system for the disposal of waste and/or hazardous materials is to apply a single heat source into a confined space in an apparatus on the assumption that the temperature within the reactor vessel of the processing system will be uniform. This assumption is without knowledge of potential cold spots which can develop within the reactor vessel of the processing system. Such systems normally gasify all of the input waste constituents; however, they do not guarantee that all such gaseous elements are subjected to the total temperature environment which is necessary to ensure total and effective destruction of the more hazardous of the waste and/or hazardous materials. A single heat source which is provided at the center of the reactor vessel processing system can create paths close to the refractory wall of the reactor vessel of the processing system whereby gaseous elements can traverse without being subjected to the required temperature/residence time combination for complete breakdown. Also, the generation of gaseous elements within the reactor vessel from the gasification process can very dramatically alter the gas flow pattern within the reactor vessel. This can result in gaseous hazardous compounds being exhausted from the reactor vessel and/or not fully processed waste constituents being transferred to slag. Downstream combustion does not achieve the full temperature capability of certain processing systems, i.e., plasma processing systems. Therefore, hazardous gaseous compounds being exhausted from the reactor vessel of the processing system result in abnormal complexity through gas handling and potentially excessive pollutants being exhausted to the atmosphere. Not fully processed waste in slag can result in some or all of this hazardous material remaining in the slag after the slag is extracted from the reactor vessel. This may mean that the slag exceeds leachate toxicity limits and, thereby, remains as a hazardous waste requiring continued special disposal or storage requirements.
Other processing systems for the disposal waste and/or hazardous materials attempt to overcome these shortcomings by dramatically increasing the overall reactor vessel temperature using plasma arc generators, thus ensuring that the minimum temperature encountered throughout the reactor vessel processing chamber is sufficient for adequate thermal decomposition of all waste constituents. This approach solves the problem of insufficient exposure of some waste constituents to the high temperature which is necessary to achieve good thermal decomposition. However, in so doing, it also creates other problems, including increased plasma generator electrode erosion, decreased reactor vessel refractory life, increased heat losses, increased electricity consumption, increased cooling load for the gas handling system and increased volatilization of pollutant elements, particularly heavy metals. The resultant higher temperature product gas on exit is not only wasteful of plasma arc generator power, but is also very conducive to increased hazardous pollutants. Such problems aggregate dramatically to reduce overall system processing efficiency and cost effectiveness.
A number of approaches have thus been developed for disposing of industrial waste products. The patent literature is replete with alleged such solutions.
U.S. Pat. No. 3,766,866, issued Oct. 23, 1973 to Krum, taught a thermal waste converter with primary and secondary chambers for the pyrolysis and combustion of waste material. Thus, this patent provided apparatus for the recycling of waste material having a pyrolyzing chamber for the gasification of waste material including an inlet for the waste and an outlet for the gas produced therefrom. An independent secondary chamber had an inlet for gas from the pyrolyzing chamber and an outlet for gases of combustion. Means connected the outlet of the pyrolyzing chamber to the inlet of the secondary chamber. Means directed solid residues from the pyrolyzing chamber to the secondary chamber. A burner in the secondary chamber burned combustible gas which is produced in the pyrolyzing chamber to reduce the solid residue in the secondary chamber to a molten condition.
U.S. Pat. No. 4,438,706, issued Mar. 27, 1984 to Boday, provided an attempt to destroy waste material using direct current (DC) arc discharge type plasma torches. This patent taught the use of DC arc discharge plasma torch in combination with an oxidizing agent for the thermochemical decomposition of certain types of waste material. The torch gas was air, and the waste material in vapor form was introduced along with oxygen downstream of the plasma arc generator, where it was heated by the torch gas. The method included transferring plasma into a plasma torch at one end of a plasma reactor. The method included introducing organic waste vapor and preheated oxygen into the torch for interaction with the plasma. The method finally included discharging end products of the interaction from the end of the plasma reactor, opposite to the location of the torch, into gas washing equipment.
Faldt, et al, U.S. Pat. No. 4,479,443, issued Oct. 30, 1984, disclosed the use of an arc discharge plasma torch thermally to decompose waste material. Waste material in the form of solid particles were introduced downstream of the arc to avoid fouling of the torch as a result of particle adherence. Oxidizing agents, e.g., oxygen and air, were mixed with the waste either before, during or after the waste was heated by the torch gas. Sufficient oxidizing agents were required for the complete oxidation of the waste material. The apparatus included a plasma generator for producing a high temperature plasma in which all molecules of the plasma reach at least a desired minimum temperature. The apparatus included means for feeding hazardous waste to and through the plasma generator. The apparatus included means for feeding sufficient oxidizing agents to the hazardous waste to permit the complete decomposition of the hazardous waste to stable products. The apparatus included means for controlling the temperature of the plasma and the flow of hazardous waste through the plasma generator so that the hazardous waste can reach a sufficiently high temperature for a sufficient period of time thermally to decompose completely to stable final products.
Barton, et al, U.S. Pat. No. 6,644,877, issued Oct. 30, 1984, disclosed the use of a DC arc plasma burner for the pyrolytic decomposition of waste. Provisions were made for feeding waste material downstream of the arc electrodes to prevent interference with the formation or generation of the plasma arc. A reaction chamber following the burner was used to combine gas and particulate matter, which is quenched and neutralized with an alkaline spray. A mechanical scrubber was used to separate gases, which are withdrawn using an exhaust fan. The apparatus included a plasma burner having a temperature in excess of 5,000xc2x0 C. The apparatus included a reaction vessel connected to the plasma burner and having a refractory lined reaction chamber for receiving the plasma arc. The apparatus included means for inserting waste material directly into the plasma arc in the co-linear electrode space to be atomized and ionized under substantially pyrolytic conditions and then recombined into recombined products in the reaction chamber. The apparatus included an outlet for removing the recombined products therefrom.
Chang, et al U.S. Pat. No. 4,886,001, issued Dec. 12, 1989, provided apparatus for pyrolytically decomposing waste material. The apparatus included a plasma torch to produce a plasma having an operating temperature of at least 5000xc2x0 C. for destroying a solution of a waste material to form a mixture of gases and solid particulate. The torch was combined with means for introducing the waste material in an atomized state. The apparatus included a recombination chamber for receiving and separating the mixture of gases and solid particulate. The apparatus included a solid separator for providing a partial vacuum for removing any carryover gases from the solid particulate.
U.S. Pat. No. 5,256,854, issued Feb. 22, 1994 to Bromberg et al, taught a method and apparatus for simultaneously bombarding toxic gases with high energy electron irradiation and rf inductive fields to destroy vaporized toxic materials. Thus, this patent provided a two-chamber system for destroying toxic waste comprising a first chamber adapted to heat and vaporize the toxic waste and a second chamber adapted to receive gases from the first chamber. The second chamber was used to break down toxic molecules in the gases via a tunable combination of simultaneous and continuous inductive heating and electron beam irradiation at no less than atmospheric pressure and at temperatures lower than those required to destroy toxic waste by inductive heating alone.
U.S. Pat. No. 5,288,969, issued Feb. 22, 1994 to Wong et al, taught an inductively coupled rf plasma torch technology operating at atmospheric pressures for the dislocation of hazardous waste. Thus, this patent provided apparatus which included a source of waste material to be processed. The apparatus included a source of gas capable of forming free electrons in a plasma when excited to a high temperature. The apparatus included combining means for combining the waste material with the gas. The apparatus included a reactor chamber. The apparatus included means for transporting the combination of the waste material and the gas through the reactor chamber. The apparatus included excitation means for exciting the gas in the reactor chamber with electromagnetic energy to form a plasma including free electrons, wherein the excitation means comprised an RF plasma torch. The apparatus included timing means for maintaining the free electrons at the raised temperature level in the reactor chamber for a sufficient time to dissociate the waste material.
U.S. Pat. No. 5,541,386, issued Jul. 30, 1996, to Mui et al, provided a system and method for the disposal of waste material including water, volatile components and vitrifiable components. The waste material was heated in a dehydrator to remove the water, was then heated in a high temperature dryer to vaporize hydrocarbon liquids, and then was fed to the focus point of a primary plasma reactor where plasma arc jets were focused on the surface of a pool of the vitrifiable components. At the focus point, the vitrifiable components were melted, and the volatile components are volatized. The melted components were received in a quench chamber where they solidified on a quench roller and were broken into chips and delivered to a receiving area. Heat from the quench chamber was transferred to the dehydrator and high temperature dryer. The hydrocarbon liquids and volatized components were fed to a secondary plasma reactor where they were disassociated into their elemental components. The effluent from the secondary plasma reactor was scrubbed to remove hydrogen sulfide and halogens, and residual components, together with excess water vapor, were extracted in an absorber and fed back for further processing in the secondary plasma reactor.
U.S. Pat. No. 5,779,991, issued Jul. 14, 1998 to Jenkins, taught an apparatus for destroying hazardous compounds in a gas stream using a cylindrical labyrinth passage wherein a plurality of electric fields were used for generating and sustaining a plasma or corona discharge through different zones within the gas labyrinth. Thus, this patent provided a mobile waste incinerator which included separate first and second zones, the first zone having a first live electrode and a ground electrode, the electrode including a first compartment and a second compartment. The mobile waste incinerator included means for exciting the first live electrode at a first electrical energy level for generating, with the first compartment, a first electric field and for generating a plasma in the waste gas when the waste gas was flowing through the first gas passage. The mobile waste incinerator included a second zone having a second live electrode mounted inside and spaced apart from the second compartment and defining, with said second compartment, a second gas passage communicating with the downstream end of the first gas passages. The mobile waste incinerator included means for exciting the second live electrode at a second electrical energy level for generating, with the second compartment, a second electric field capable of sustaining the plasma in the waste gas when the waste gas was flowing through said second gas passage. The mobile waste incinerator included means for generating a third electric field between the second live electrode and the first live electrode for providing a complementary source of electrical energy between the first and second electric fields for sustaining the plasma between the first and the second zones.
U.S. Pat. No. 5,798,496, issued Apr. 22, 2003, to Eckhoff et al, taught a mobile plasma-based waste disposal system which utilized an arc-torch plasma technology to dispose of industrial waste. The portable reactor included a rotatable kiln comprising an upper end for introduction of waste material and a lower end, said rotatable kiln mounted on a movable vehicle. It included a breech disposed adjacent the lower end of the kiln, at least one of the breech and lower end forming an outlet for discharge of pyrolytically treated waste material. It includes at least two plasma guns attached to the breech and disposed so as to direct an arc into the kiln. It included at least two target electrodes spaced from the plasma guns and attached to at least one of the breech an the kiln. At least one of the plasma guns and at least one of the target electrodes was movable.
U.S. Pat. No. 6,552,295, issued Apr. 22, 2003, to Markunas et al provided a method and apparatus for plasma waste disposal of hazardous waste material, where the hazardous material was volatilized under vacuum inside a containment chamber to produce a pre-processed gas as input to a plasma furnace including a plasma-forming region in which a plasma-forming magnetic field was produced. The pre-processed gas was passed at low pressure and without circumvention through the plasma-forming region and was directly energized to an inductively-coupled plasma state such that hazardous waste reactants included in the pre-processed gas were completely dissociated in transit through the plasma-forming region. Preferably, the plasma-forming region was shaped as a vacuum annulus and was dimensioned such that there was no bypass by which hazardous waste reactants in the pre-processed gas can circumvent the plasma-forming region. The plasma furnace was powered by a high frequency power supply outputting power at a fundamental frequency. The power supply contained parasitic power dissipation mechanisms to prevent non-fundamental, parasitic frequencies from destabilizing the fundamental frequency output power.
The prior art plasma waste decomposition systems described above suffered from a variety of shortcomings. One shortcoming results from the fact that the waste material generally cannot be introduced directly into the plasma arc because such introduction causes contamination of the arc electrodes and subsequent erratic operation of the arc. Thus, the waste material was introduced downstream of the arc and was indirectly heated by the torch gas. This technique shortened the high temperature residence time of the waste material, resulting in incomplete decomposition.
Further, the performance of the plasma arc is highly sensitive to the flow rate of the waste and carrier gas. Thus, the flow rates must be confined within narrow limits, leading to difficulties in controlling and maintaining system performance. Arc electrode erosion with use further complicated the maintenance, operation, stability and safety of the system. Small scale operation of DC arc plasmas was also very inefficient due in part to the minimum gas flow rate and electric power requirements needed to strike initiate and sustain the arc. Scaling the prior art systems for operation at different waste throughput levels and with a variety of waste materials has proven to be difficult, requiring major system configuration changes which are expensive to accomplish.
Additionally, the need for organic, oxidizing, and/or reducing agents to be confined with the waste material in the prior art systems often resulted in highly undesirable compounds in the waste residue.
In summary, none of the prior art systems have provided a consistent method of reducing all types and forms of hazardous waste to compounds which were suitable for environmental disposal.
It is therefore an object of a broad aspect of the present invention to address these shortcomings and to provide hazardous waste processing systems and methods which ensure total destruction of all hazardous constituents while maintaining a low input power level and a long refractory life.
One broad embodiment of the present invention provides an apparatus for the disposal of waste and/or hazardous materials. The apparatus includes a refractory-lined reactor vessel. The apparatus includes plasma-generating means within the refractory-lined reactor vessel for producing a high temperature plasma processing zone which has a substantially-uniform high temperature across the entire periphery of the refractory-lined reactor vessel. The plasma-generating means includes at least one fixed-position plasma arc generator, and at least one movable plasma arc generator. The apparatus includes first feeding means for feeding the waste and/or hazardous materials to, and through, the high temperature plasma processing zone. The apparatus includes second feeding means for feeding sufficient process additive agents to the high temperature plasma processing zone to cause the complete decomposition of the waste and/or hazardous materials and the formation of stable, non-hazardous materials. The apparatus includes controlling means for controlling the plasma arc generating means and the flow of the waste and/or hazardous materials through the high temperature plasma processing zone to assure that all the waste and/or hazardous material reaches a sufficiently high temperature, and for a sufficient period of time, thermally to fully decompose the waste and/or hazardous materials into very small ions. Adequate process additives are made available to establish the optimum chemical equilibrium that will convert the decomposition products into stable non-hazardous final products. The apparatus includes gas removal means for removing product gas from the reactor vessel. The apparatus includes monitoring means for monitoring the gas stream to determine the amount of particulate matter in the product gas stream. The apparatus includes solids removing means for removing solid stable non-hazardous final product in a lava like state from the apparatus.
A second broad embodiment of the present invention provides a method for the disposal of waste and/or hazardous materials. The method includes providing a refractory-lined cylindrical reactor vessel with plasma-generating means within the refractory-lined reactor vessel and producing a high temperature plasma processing zone therein which has a substantially-uniform high temperature across the entire periphery of the refractory-lined reactor vessel, by way of plasma-generating means which includes at least one fixed-position plasma arc generator, and at least one movable plasma arc generator. The method includes feeding, preferably continuously, solid and/or liquid waste and/or hazardous materials to, and through, the high temperature plasma processing zone. The method includes selectively, preferably continuously, feeding sufficient process additive agents to the high temperature plasma processing zone, for completely decomposing the waste and/or hazardous materials and to form stable, non-hazardous materials. The method includes removing, preferably continuously, gaseous products from the refractory lined reactor vessel. The method includes monitoring, preferably continuously, the gaseous products to determine the amount of particulate material in the gaseous products. The method includes removing solid stable non-hazardous final product from the refractory-lined reactor vessel.
By a first feature of the apparatus embodiment of the present invention the at least one fixed position plasma arc generator is a plurality of, e.g., two, fixed position plasma arc generators, which are disposed within the refractory-lined reactor vessel from opposite sides thereof, with angular displacement relative to each other in order for their plasma plumes to intersect at a focal point which is near the center of the waste and/or hazardous material input into the apparatus.
By a second feature of the apparatus embodiment of the present invention, the at least one movable plasma arc generator is a single moveable plasma arc generator which is mounted at the top of the refractory-lined reactor vessel and which has three degrees of freedom to permit aiming towards the focal point of the plasma arc plumes from the fixed position plasma arc generators or towards the molten slag pool.
By a third feature of the apparatus embodiment of the present invention, the first feeding means comprises a plurality of waste and/or hazardous material feed ports, each of which is configured to feed directly towards the focal point of the plasma arc plumes from the fixed position plasma arc generators.
By a fourth feature of the apparatus embodiment of the present invention, the gas removal means and the solids removal means are ports which are diametrically opposite to the first feeding means.
By a fifth feature of the apparatus embodiment of the present invention, the apparatus includes at least one port for the injection of steam towards a point which is just past the intersection focal point of the plasma arc plumes from the fixed position plasma arc generators, on the opposite side from the feed inlet. It also includes a steam injection port covering the gas exit area.
By a sixth feature of the apparatus embodiment of the present invention, the feeding means comprises a plurality of air inlet ports disposed in spaced-apart relation around the refractory-lined reactor vessel.
By a seventh feature of the apparatus embodiment of the present invention, the gas removal means comprises a gas outlet conduit which is configured to produce an exit velocity of the gas conducive for airborne solids to fall back into the reactor vessel rather than be carried out of the reactor vessel by the exiting gas stream.
By an eighth feature of the apparatus embodiment of the present invention, a lower section of the refractory-lined reactor vessel is flanged to enable connection of a removable bottom element to the remainder of the refractory-lined reactor vessel to facilitate opening.
By a ninth feature of the apparatus embodiment of the present invention, the refractory lining comprises materials similar to AP. Green G26LI, G23LI, G20LI and Insulblok 19.
By a tenth feature of the apparatus embodiment of the present invention, a lower section of the refractory-lined reactor vessel consists of a hot face refractory, the hot face refractory comprising materials similar to RADEX COMPAC-FLO V253 or DIDIER RK30.
By an eleventh feature of the apparatus embodiment of the present invention, the apparatus includes optional water cooling means for the lower section of the refractory-lined reactor vessel.
By a twelfth feature of the apparatus embodiment of the present invention, the monitoring means includes sensors which are configured to determine the opacity of the exit gas stream.
By a thirteenth feature of the apparatus embodiment of the present invention, the sensors are maintained essentially-deposit free by a nitrogen purge element which is configured to provide a flow of nitrogen across the face of the sensors.
By a fourteenth feature of the apparatus embodiment of the present invention, the sensors are maintained essentially-deposit free by an element which is configured to maintain a negative pressure in the region of the sensors.
By a fifteenth feature of the apparatus embodiment of the present invention, the apparatus also includes a removable preheat burner within the refractory-lined reactor vessel.
By a sixteenth feature of the apparatus embodiment of the present invention, the refractory-lined reactor vessel is cylindrical.
By a first feature of the method embodiment of the present invention, the method includes disposing the at least one movable plasma arc generator in close proximity to the ports which feed the waste and/or hazardous materials to, and through, the high temperature plasma processing zone.
By a second feature of the method embodiment of the present invention, the method further includes injecting steam towards the high temperature plasma zone and towards the gas exit area.
By a third feature of the method embodiment of the present invention, the method comprises disposing air inlet ports in spaced-apart relation around the refractory-lined cylindrical vessel and selectively feeding the process additive agents into the high temperature plasma processing zone through the inlet ports.
By a fourth feature of the method embodiment of the present invention, the method further comprises creating an exit velocity of the gaseous products which is conductive for airborne solids to fall back into the reactor vessel as opposed to being carried out of the reactor vessel by the exiting gas stream.
By a fifth feature of the method embodiment of the present invention, the method includes the option of cooling a lower section of the refractory-lined cylindrical vessel.
By a sixth feature of the method embodiment of the present invention, the method includes monitoring of the gaseous products by determining the opacity of the gaseous products by opacity sensors.
By a seventh feature of the method embodiment of the present invention, the method further comprises maintaining the opacity sensor elements essentially deposit free by flowing a stream of nitrogen across the face of the sensor elements.
By an eighth feature of the method embodiment of the present invention, the method further comprises maintaining the opacity sensors essentially deposit free by maintaining a negative pressure in the region of the sensors.
By a ninth feature of the method embodiment of the present invention, the method further comprises the first step of preheating the refractory-lined cylindrical vessel by means of a removable burner system.
The present invention preferably entails the use of multiple, e.g., two, fixed position plasma arc generators for primary processing and a single movable plasma arc generator for secondary or processing assistance and/or for final conditioning of the slag prior to exit from the apparatus, i.e., reactor vessel. As will be described hereinafter, the present invention provides control of reactor vessel geometry to ensure maximum processing efficiency. Positioning and operation of the plasma arc generators provides for a high temperature processing zone where it is optimally required, as well as to provide adequate heat concentration to melt and force the slag to flow, in addition to achieving the lowest possible product gas temperature at the product gas exit port.
Most complete breakdown of waste and/or hazardous materials is achieved if a high temperature processing zone is maintained as a solid wall across the entire periphery of the reactor vessel to ensure that all input waste and/or hazardous materials are forced to go through it. In aspects of the present invention, the fixed position plasma arc generators for primary processing are provided in the reactor vessel at opposite sides of the reactor vessel with angular displacement relative to each other and aimed to permit their plasma plumes to intersect at a focal point and provide fullest temperature coverage of the hazardous waste feeder opening into the reactor vessel. The focal point of the plasma arc plumes from these plasma arc generators is preferably fixed near the center of the input waste. They can also be adjusted so as to ensure the maintenance of the optimal high temperature processing zone as well as to induce advantageous gas flow patterns around the entire reactor vessel. The moveable plasma arc generator is preferably mounted in the top of the reactor vessel and possesses three degrees of freedom to permit aiming of its plasma arc plume at, or around, the intersection of the plasma arc plumes from the fixed position plasma arc generators to provide secondary, or assisted processing should the need arise. It may also permit aiming of its plume towards the slag pool at, or around, the slag exit port for slag conditioning. Secondary processing assistance from the moveable plasma arc generator is advantageous through periods of lowering processing temperature due to unexpected changes in the chemical composition characteristics of the input waste and/or hazardous material. Slag conditioning is essential to ensure that the slag exit port remains open through the complete slag extraction period and to maintain the slag as homogeneous as possible to guard against the possibility that some incompletely-processed material may inadvertently make its way out of the reactor vessel during slag extraction. All plasma arc generators may be operated on a continuous basis at the discretion of the operator.
The reactor vessel physical design characteristics are determined by a number of factors, namely:
Firstly, the chemical composition of the waste and/or hazardous material stream to be processed. The internal configuration and size of the reactor vessel are dictated by the operational characteristics through analyses of the input waste stream to be processed.
Secondly, the plasma arc generators. The plasma arc generators must be positioned within the reactor vessel at the desired depth in order to concentrate the high temperature processing zone where it will be most effective, while at the same time minimizing plasma arc generator heat loses.
Thirdly, the position and orientation of the plasma arc generators. The plasma arc generators must be positioned, and their plasma heat must be directed, in such a way as to ensure an adequate travel path for all gaseous molecules produced. This is to maintain a sufficient residence time in the high temperature processing zone to guarantee their full decomposition, and conversion into the smallest and most non-polluting molecules.
Fourthly, the position, orientation and number of the process additive injection ports. The process additives must be injected where they will ensure most efficient reaction to achieve the desired conversion result.
The waste feed location, the plasma arc generators insertion depth, their position and orientation, and the position, orientation and number of the process additive ports are all important in establishing the desired flow and temperature distribution features that are critical in minimizing refractory erosion with the best possible compromise of a temperature profile, i.e. very high temperature processing zone, high temperature slag melting/tapping zone and medium temperature gas exit. This generalized description of the present invention may be represented by an embodiment which includes the following features with the overall objective of:
1. full decomposition of the waste in order to achieve minimization of pollutants;
2. full melting and homogenization of the slag, and
3. minimization of exhaust heat loses.
The embodiment includes two opposing side mounted plasma arc generators with center line angular displacement and a combined plasma arc plume fixed focal point close to the center of the input waste and/or hazardous material stream. The angular displacement provides for turbulence within the input waste and the generated product gas substantially to assist in the efficiency of processing. The fixed focal point generates a total wall of high temperature processing zone through which all elements of the input waste are forced to pass.
The embodiment includes a top mounted plasma arc generator with three degrees of freedom to permit the plasma arc plume from this generator to be directed to supply plasma heat in support of the side mounted processing plasma arc generators, or to be directed to be concentrated on the slag pool at and around the slag exit port. This plasma arc generator is mounted at the rear of the reactor vessel, diametrically opposite to the incoming waste front and in close proximity to the by-product exit ports to ensure the maintenance of the fill required processing temperature for both of the process by-products.
The embodiment includes a plurality of input waste feed ports to cater to any physical characteristics of the input waste and/or hazardous waste materials, each of which feed directly into the high temperature processing zone focal area as created by the plasma arc plumes from the side mounted plasma arc generators.
The embodiment includes slag exit port and product gas outlet conduit diametrically opposite to the feed ports to ensure the maximum path possible for both the solid and gaseous process by-products for maximum processing efficiency for hazardous constituent destruction. This gas outlet conduit is vertically positioned and is configured for a gas exit velocity conducive for airborne solids to fall back into the reactor vessel as opposed to being carried out of the reactor vessel with the exiting gas.
The embodiment includes a plurality, e.g., up to three, process additive input ports for steam injection, these ports being strategically located to direct steam into the high temperature processing zone and into the product gas mass just prior to its exit from the reactor vessel.
The embodiment includes a plurality, e.g., up to five, process additive input ports for air injection, these ports being strategically located in and around the reactor vessel to ensure fill coverage of process additives into the processing zone.
The embodiment includes a flanged lower section of the reactor vessel which is connected to a flanged main section of the reactor vessel to facilitate opening of the reactor vessel for refractory inspection and repair as the need might arise.
The embodiment includes a layer of up to seventeen inches, or more, of specially selected refractory lining throughout the entire reactor vessel to ensure maximum retention of processing heat while being impervious to chemical reaction from the input waste stream and processing intermediate chemical constituents.
The embodiment includes a plurality, e.g., up to four, CCTV ports to maintain operator full visibility of all aspects of processing.
The type and quantity of the process additives are very carefully selected to optimize input waste hazardous constituent destruction while maintaining adherence to regulatory authority emission limits and minimizing operating costs. Steam input ensures sufficient free oxygen and hydrogen to maximize the conversion of decomposed elements of the input waste into fuel gas and/or non-hazardous compounds. Air input assists in processing chemistry balancing to maximize carbon conversion to a fuel gas (minimize free carbon) and to maintain the optimum processing temperatures while minimizing the relatively high cost plasma arc input heat. The quantity of both additives is established and very rigidly controlled as identified by the outputs for the waste being processed. The amount of air injection is very carefully established to ensure a maximum trade-off for relatively high cost plasma arc input heat while ensuring the overall process does not approach any of the undesirable process characteristics associated with incineration, and while meeting and bettering the emission standards of the local area.
It has been found through many years of plasma gasification processing that the amount of particulate matter in the product gas stream has a direct relationship to the emission rate of polluting elements. Pollutants tend to adhere to particulate matter, which assists their exit from the reactor vessel and through the exhaust piping. It has been found that minimizing the amount of particulate matter in the gas stream also minimizes the emission rate for most pollutants. One manner of determining changes in the amount of particulate matter in the gas stream is to monitor the gas stream opacity and establish a baseline for an acceptable concentration in accordance with regulatory authority restrictions within the location of processing. Thereafter, real-time feedback of opacity within the product gas piping provides a mechanism for automation of process additive input rates, primarily steam, to maintain the level of particulate matter below the maximum allowable concentration.
In order to optimize the operation of the opacity monitors, it is desirable to maintain sensor elements which are free of deposits therein to ensure accuracy of readings. The prevention of deposition on the sensor elements is achieved by either of two methods: firstly, the provision of a small amount of nitrogen across the face of each element to prevent airborne particles from settling; secondly, the maintenance of a slightly negative pressure in this portion of the gas handling system to ensure airborne particles are drawn past the sensor elements. Typically, nitrogen is used unless it will be detrimental to the chemical composition of the gas stream depending on the waste stream being processed and the potential use to be made of the gas on exit.
The flanged lower section which is connected to the flanged main upper section of the reactor provides for the ease of inspection and repair of the refractory lining as the need might arise. The refractory lining in the bottom section of the reactor vessel is much more prone to wear and deterioration since it must withstand higher temperatures from the operating plasma arc generators and it is continuously in contact with the hot molten slag. The refractory in the lower section is, therefore designed to consist of a more durable xe2x80x9chot facexe2x80x9d refractory than the refractory on the reactor vessel walls and top. For example, the refractory on the walls and top can be made of DIDIER RK30 brick, and the different xe2x80x9chot facexe2x80x9d refractory for the lower section can be made with RADEX COMPAC-FLO V253.
In other embodiments, the lower section may also be water cooled, preferably through the outer shell, to prevent abnormal deterioration of the refractory lining. A duplicate lower section may also be constructed to facilitate faster return of the processing facility to operational status through periods of refractory repair or to provide for alternate construction to accommodate processing of more demanding and/or corrosive input waste streams.
Process control may be automated through up to three operational characteristics, namely: reactor vessel pressure changes attributable to a non-optimal feed rate, input waste stream chemical characteristic changes or constrictions in the product gas handling system due to the build up of solid deposits; reactor vessel and product gas temperature changes attributable to a non-optimal feed rate or input waste stream chemical characteristic changes; and product gas opacity reading increases attributable to non-optimal processing and/or input waste stream chemical characteristic changes.
Other embodiments of the present invention may include varying numbers of plasma arc generators, steam injection ports, air injection ports and CCTV ports depending on the waste stream under consideration and the desired operational characteristics.